1. Field of the Invention
This invention is concerned with thermally stable, high tenacity, high modulus polyesters prepared from aromatic dibasic acids and thermally stable, rigid bisphenols containing no aliphatic beta-hydrogen atoms.
2. Description of the Prior Art
Polyester fibers such as those spun from polyethylene terephthalate have found wide commercial acceptance. These fibers, however, generally have limited thermal stability. A major pathway for thermal decomposition of known aliphatic-aromatic polyesters is thermal elimination at the site of aliphatic beta-hydrogens.
Polyesters having improved thermal stability have been prepared from terephthalic acid and neopentyl glycol. These polymers do not contain aliphatic beta-hydrogens. Such polyesters are described in British Pat. No. 828,922, French Pat. No. 1,392,313 and U.S. Pat. Nos. 3,194,794 and 3,498,952. These polyesters, however, are amorphous and thus have limited strength as fibers.
Komatsu et al in U.S. Pat. No. 3,705,130 show polyesters of the formula ##STR5## in which m is 2 or 4, n is 4 or 6, and n is larger than m. These polyesters are prepared by reaction of a compound of the formula ##STR6## with a diol of formula HO--(CH.sub.2).sub.n --OH. In this reaction there may be present up to 25% of many other dicarboxylic compounds and diols, including specifically terephthalic acid and neopentyl glycol. Fibers having melting points of 180.degree.-300.degree. C are obtained. The highest Initial Young's Modulus reported for these fibers is 61 grams per denier.
It would be desirable to provide new polyesters of superior thermal stability which could be melt spun into fibers characterized by high tenacity and high modulus. Such fibers would be useful, for example, as tire cords.